An electrical junction box (relay box), which is provided in an automobile or the like, has a component mounting surface on which components such as a relay are mountable. In a conventional electrical junction box, electrical components are mounted directly on the component mounting surface. Mounting electrical components directly on the electrical junction box, however, requires that design of the electrical junction box be changed each time the electrical component to be mounted is changed. This raises a problem that the electrical component to be mounted cannot easily be changed.
Recently, therefore, a configuration is sometimes adopted in which a unit having electrical components mounted thereon is detachably mounted to the electrical junction box in a cassette-like manner. With such a configuration, the electrical components to be mounted can be easily changed by changing the unit. This configuration is shown in, for example, Patent Documents 1 and 2.
The electrical junction box shown in Patent Document 1 includes a base with a mount to which either one of a relay block and a relay module is selectively mountable. According to Patent Document 1, the relay block and the relay module are configured to be compatible such that they are mountable on the same mount, and thus the relay block and the relay module can be used differently as appropriate, which enables a flexible design.
The electrical junction box shown in Patent Document 2 allows an electrical circuit unit to be inserted therein from the lower side of a receiving part (paragraph 0033 of Patent Document 2). The electrical junction box shown in Patent Document 2 allows the electrical circuit unit received in the receiving part to be taken out upward (paragraph 0035). The electrical junction box shown in Patent Document 2 also allows an electrical circuit unit to be inserted therein from the upper side of the receiving part (paragraph 0036).